It is known to encapsulate hydrophobic liquids by dispersing the hydrophobic liquid into an aqueous medium containing a melamine formaldehyde pre-condensate and then reducing the pH, resulting in an impervious aminoplast resin shell wall surrounding the hydrophobic liquid. Such microcapsules are preferably used to provide encapsulated inks for use in pressure sensitive carbonless copy paper. However, since these microcapsules are based on melamine formaldehyde resins, there is a risk that under certain conditions formaldehyde may be evolved, which is undesirable.
U.S. Pat. No. 5,234,711 describes a method for encapsulation of pigment particles utilized in ink formulations and their use for cosmetic products. The cosmetic products are especially directed to eye liner pens.
U.S. Pat. No. 5,382,433 and published PCT Application WO 98/5002 describe the use of a cosmetic stick that contains microencapsulated pigment particles. The encapsulated pigment in the '433 patent is made by coacervation polymerization. The PCT application expands on this patent by including a volatile solvent in the cosmetic composition. The volatile solvent is represented to minimize the gritty feel of the microencapsulated material.
A variety of techniques are known for providing encapsulated or entrapped colorants. For example, published PCT Application WO 91/06277 describes cosmetic formulations which have activatable dormant pigments dispersed in an anhydrous base or vehicle. Ground pigment or liquid carrier dispersion is microencapsulated to form stable, dry, free flowing powder of micro-sized particles. The preferred process of encapsulation is by coacervation e.g. by emulsifying a liquid dispersion in a continuous, external aqueous phase to form micro-sized droplets and a complex of colloidal material is added to the external phase in such a way to form a deposit on or around each droplet thereby forming an outer wall or shell. The microcapsules are intended to rupture and release the dormant pigment when subjected to physical forces.
U.S. Pat. No. 5,234,711 concerns methods of encapsulating pigment particles useful in manufacturing of cosmetic products. It is an objective of this disclosure to employ an encapsulation process for increasing the wettability, dispersibility and heat resistance of the pigment particles. The method encapsulation involves redox or free radical vinyl polymerization in an aqueous medium.
Published European Patent Application 225,799 describes microencapsulated solid non-magnetic colorant material in a liquid, gel, waxy or low temperature melting solid carrier phase, which is encapsulated within a polymeric shell. Absorbed onto the shell is a silane or titanate coupling agent, which increases the oleophilicity of the surface of the solid colorant material.
Published European Patent Application 445,342 relates to a cosmetic composition comprising a pigment that has been formed by incorporating a solvate dye into a resin and admixing with a cosmetic carrier. The amount of pigment present is sufficient to provide attractive amount of pigment present sufficient to provide an attractive cosmetic effect when applied to skin, nails or hair. Any cosmetically acceptable soluble dye can be used. Any resin may be used provided it can be pulverized to a fine powder. The solvate dye may be incorporated into the resin by adding to the elasticized or molten resin, or by dissolving the dye in a solution of unpolymerized resin and mutual solvent for the dye and the resin, then polymerizing the resin, or by contacting the dye with the resin. The dye impregnated resin powders are said to be used in a variety of cosmetic compositions
WO 02/090445 addresses the problem of color retention and provides polymeric particles comprising a matrix polymer and colorant distributed throughout it. The matrix polymer is formed from a blend of monomers comprising a first monomer, which is an ethylenically unsaturated ionic monomer, which is a salt of a volatile counterion, and a second monomer, which is an ethylenically unsaturated hydrophobic monomer, which is capable of forming a homopolymer of glass transition temperature in excess of 50° C. Typical matrix polymers include copolymers that have been formed from styrene with ammonium acrylate. The polymeric particles exhibit good retention properties and are able to retain the colorant under a variety of conditions. The obtained particles are stated to be useful in a variety of industrial processes, for instance in the manufacture of inks, paper and cosmetics.
The prior art does not describe the use of a blend of microencapsulated coloring agents in cosmetic compositions that produce a textured natural tone coloring when applied, or creates similar effects on or in the cosmetic product itself.